Major UI refresh: sidebar redesign, theme expansion, and chat performance optimizations (#706)

## Summary
Complete sidebar redesign and comprehensive UI polish pass with performance optimizations, theme system refinements, and desktop integration improvements.

## Key Changes

**Sidebar & Navigation Redesign**
- Redesigned sessions sidebar layout with unified button primitives
- Added activity sections with project grouping and improved session organization
- Refined sidebar corners, spacing, and visual hierarchy
- Removed NavRail component in favor of streamlined sidebar
- Stabilized sessions bar toggle position in fullscreen mode

**Performance Optimizations**
- Reduced chat streaming CPU usage and storage churn
- Optimized task tool polling and live timers with debouncing
- Prevented chat state races and reduced background request load
- Debounced draft writes and coalesced session reloads
- Optimized message store updates and turn tracking

**Theme & Visual System**
- Added theme-aware window corners (desktop) and border radius tokens
- Introduced glassmorphism effects on desktop sidebar
- Added backdrop blur to UI elements

**Chat Experience**
- Added session-based permission auto-accept toggle in chat input
- Polished permission shield UX with improved icon sizing and spacing
- Fixed chat scroll-to-bottom behavior and timeline tracking
- Enhanced tool output display with better path label detection
- Removed duplicate draft context details in chat header
- Added text selection menu to chat messages

**Git Improvements**
- Refreshed git history visual design with cleaner dividers
- Added remote removal action in sync selector
- Stabilized git polling to prevent excessive requests
- Improved tool output rendering for git operations

**Settings & Panels**
- Fixed mobile scrolling on settings pages
- Made outside-click settings close instantly
- Reduced settings load churn and CPU spikes
- Improved services dropdown layout and spacing
- Softened panel resize handles

**Desktop Integration**
- Synced macOS window theme with app theme
- Restored window dragging in sidebar header zones
- Fixed system window corners on macOS
- Improved header session metadata and action controls

**Button & Component Standardization**
- Unified button primitives across all components
- Standardized destructive action patterns
- Removed unused button variants (button-large, button-small)
- Aligned context tab close hit areas

---------

Co-authored-by: Iuliia Ivashko <yulia.ivashko@gmail.com>

packages/ui/src/components/session/sidebar/hooks/useSessionGrouping.ts

@@ -19,6 +19,8 @@ type Args = {
   isVSCode: boolean;
 };
 
+const isArchivedSession = (session: Session): boolean => Boolean(session.time?.archived);
+
 export const useSessionGrouping = (args: Args) => {
   const buildGroupSearchText = React.useCallback((group: SessionGroup): string => {
     return [group.label, group.branch ?? '', group.description ?? '', group.directory ?? ''].join(' ').toLowerCase();
@@ -70,6 +72,10 @@ export const useSessionGrouping = (args: Args) => {
       sortedProjectSessions.forEach((session) => {
         const parentID = (session as Session & { parentID?: string | null }).parentID;
         if (!parentID) return;
+        const parentSession = sessionMap.get(parentID);
+        if (!parentSession || isArchivedSession(parentSession) !== isArchivedSession(session)) {
+          return;
+        }
         const collection = childrenMap.get(parentID) ?? [];
         collection.push(session);
         childrenMap.set(parentID, collection);
@@ -105,7 +111,9 @@ export const useSessionGrouping = (args: Args) => {
       const roots = sortedProjectSessions.filter((session) => {
         const parentID = (session as Session & { parentID?: string | null }).parentID;
         if (!parentID) return true;
-        return !sessionMap.has(parentID);
+        const parentSession = sessionMap.get(parentID);
+        if (!parentSession) return true;
+        return isArchivedSession(parentSession) !== isArchivedSession(session);
       });
 
       const groupedNodes = new Map<string, SessionNode[]>();